This application relates to a multi weir tank for use with a multi-phase bath for plating of a substrate or similar type use. More particularly, it relates to a tank having entrance ducts wherein items to be exposed to lower phases of multi-phase baths may enter and exit the lower layers of the bath without coming into contact with the upper layer.
In certain preplating processes, it is useful to use a two layer bath comprising a lower layer or phase of preplating solution and an upper layer or phase of liquid which is not miscible with the lower layer. As an example, water can be used to cover the trichloroethylene/phosphorus sesquisulfide preplating solution disclosed and claimed in U.S. Pat. No. 3,650,708. The water serves the function of preventing the preplating solution from evaporating and filling the surrounding environment with fumes.
Tanks having weirs are well known in the plating art, and are used to circulate both liquids in the two-layer bath while maintaining the integrity of the two levels. One problem with such tanks holding two layer baths is that an article which is to be subjected to the lower solution must also come in contact with the surface solution. Although this is sometimes a desirable feature, in certain instances it is not.
One proposed solution to the problem of covering the lower solution while maintaining openings in the surface through which articles may pass without contacting the covering solution is the apparatus shown in FIG. 1. This apparatus basically consists of a tank 11 having a weir (as described above) and also having two tubes 15, 17 which are held in place by mechanical means (not shown) in a geometrical arrangement which approximates a V shape as shown in the drawing. Once these tubes are placed in the solution, the surface layer 31 must be removed from each tube by mechanical means. When the plating operation ceases, and it is desired to cover the lower solution 33 with the surface solution 31, the solution must either be added by mechanical means, or alternatively, the tubes may be removed.
In operation of the above-described apparatus, an article to be subjected to the lower solution enters the bath through tube 15 and exits through tube 17. In a preferred use, a pulley 41 is present at the bottom of the tank midway between the bottom end of each tube. Wire cable 35 having a plastic sheath which is to be treated is advanced over pulley 43, into tube 15, over pulley 41, out of tube 17 and over pulley 45. In this manner, most of the lower solution 33 remains covered by surface solution 31 while the cable 35 comes in contact only with the plating solution 33.
When the above-described apparatus was used in small quasi-commercial applications of an experimental nature, the disadvantages of this apparatus for large scale commercial use became apparent. One such disadvantage to a commercial operation is the labor required to manually remove the surface solution from the tubes each time the apparatus is placed in use, and replacing the surface solution each time the plating operation is discontinued. Accordingly, one of the objects of the invention is to provide a tank in which most of the plating solution is covered during plating operations while leaving uncovered a large enough portion of the plating solution to accept an article without the article contacting the surface solution. It is another object of the invention to automatically cover the entire plating solution with surface solution when the apparatus is shut down, and also to automatically uncover much of the plating solution as is desired when the apparatus is put in operation.